Yes, minors need a birth certificate to fly on United Airlines. So, when you choose to travel with babies under 2 years of age on a United flight, then you can add the same by selecting the “Infant on lap” option either at the time of reservation or check-in, and they have to present a birth certificate for age verification. However, the United Airlines Unaccompanied Minor Policy also states that if an adult is traveling with more than one infant, then an additional child could need their own tickets.